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Research
The Cabauw Infrasound Array
Gravity wave detection with CIA
- Uncertainties in the representation of the atmospheric stable boundary layer(SBL) in climate models contribute to uncertainties in climate prediction. The strength of turbulent mixing in the SBL, that atmospheric models need to perform well, is different from what is observed in field experiments.
Turbulence is the dominating mechanism for transport in the weakly stable boundary layer. When the SBL becomes more stable, tubulence is surpressed and other processes like low level jets, radiation and gravity waves may become important.
- Gravity waves may occur in atmospheric layers which are stably stratified. They transport energy and momentum and by breaking the wave energy may be transferred into turbulent energy. Under certain conditions gravity waves may have important effects on the structure and dynamics of the SBL. Turbulence in a SBL itself may generate gravity waves. This process may account for the difference in transport properties of momentum and scalar quantities in the very SBL expressed as a turbulent Prandl number different from 1. Disturbances above the SBL may also induce gravity waves. When these waves break they may enhance mixing in the SBL.
- For the interpretation of observations in the SBL at Cabauw it is important to have information on the gravity wave activity. Gravity waves show their presence by coherent fluctuations in pressure, wind speed and temperature and thus can be detected accordingly with pressure transducers, wind instruments or temperature sensors. To discriminate gravity waves from turbulence and other disturbing influences, the coherence in space and/or time have to be exploited.
- The CIA is an excellent instrument for the detection of gravity waves and in this respect an important addition to the instrumentation at Cabauw. Furthermore, three temperature sensors will be mounted in an equilateral triangle with a base of 17 m at a level in the 200 m tall tower. With both instruments frequency and horizontal wave vector of gravity waves can be determined.
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